SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3 Page 61 The X-Ray Knee Instability and Degenerative Score (X-KIDS) to determine the preference for a partial or a total knee arthroplasty (PKA/TKA) CR Oosthuizen MBChB(Stell), MMed(Ortho) Orthopaedic surgeon, Wilgeheuwel Hospital, Roodepoort, Johannesburg S Burger MBChB(Pret), Neurosurgery(SA) Specialist neurosurgeon, Wilgeheuwel Hospital, Johannesburg DP Vermaak MBChB (Pret), MSc(Sport Med)(Pret), MMed(Orth)(UOFS), Arthroplasty Fellowship UK Little Company of Mary Hospital, Pretoria P Goldschmidt MBBCh FFRad(D)(SA) Radiologists: Van Rensburg and Partners SA (Inc) R Spangenberg BCom (Unisa)(Risk Management) Independent Statistical Consulting Services: Maryn Viljoen Corresponding author: Dr CR Oosthuizen PO Box 3158 Honeydew 2040 Tel: 011 794 3371 Fax: 011 794 3368 Email: [email protected]Abstract The X-ray Knee Instability and Degenerative Score (X-KIDS) was developed as a tool based on the degenerative and instability patterns seen on routine X-ray views of the weight-bearing compartments and tested on 336 knees, average age 64 years and followed up for 24 months. It is a study to evaluate the X-KIDS scoring method, which quantifies whether a PKA or TKA is the procedure of choice, comparing it to the surgical procedure done and to a stress X-ray evaluation as a stand-alone when contemplating knee arthroplasty. Points are allocated to the following features: narrowing (N), osteophytes (O), and subluxations (S). The assessed score is out of 10. A patient with a score of at least 3 but less than 5 is suitable for a PKA, a score of 5 could be suitable for a PKA or a TKA and a score exceeding 5 requires a TKA. There was a 95.82% (321) evaluator consensus with the X-KIDS on the X-ray sequence for a PKA or TKA. 92.3% (310) received the procedure assessed by X-KIDS and 2.98% (10) could have received the procedure evaluated. 90.78% of the stress views indicated the preferred procedure and is not as reliable as X-KIDS to determine the procedure. Key words: knee, arthroplasty, degenerative, instability, X-ray score http://dx.doi.org/10.17159/2309-8309/2015/v14n3a7
Transcript
SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3 Page 61
The X-Ray Knee Instability andDegenerative Score (X-KIDS) to determinethe preference for a partial or a total knee
AbstractThe X-ray Knee Instability and Degenerative Score (X-KIDS) was developed as a tool based on the degenerativeand instability patterns seen on routine X-ray views of the weight-bearing compartments and tested on 336 knees,average age 64 years and followed up for 24 months.
It is a study to evaluate the X-KIDS scoring method, which quantifies whether a PKA or TKA is the procedureof choice, comparing it to the surgical procedure done and to a stress X-ray evaluation as a stand-alone whencontemplating knee arthroplasty.
Points are allocated to the following features: narrowing (N), osteophytes (O), and subluxations (S).The assessed score is out of 10. A patient with a score of at least 3 but less than 5 is suitable for a PKA, a score
of 5 could be suitable for a PKA or a TKA and a score exceeding 5 requires a TKA.There was a 95.82% (321) evaluator consensus with the X-KIDS on the X-ray sequence for a PKA or TKA.92.3% (310) received the procedure assessed by X-KIDS and 2.98% (10) could have received the procedure
evaluated. 90.78% of the stress views indicated the preferred procedure and is not as reliable as X-KIDS to determine the
Page 62 SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3
IntroductionDue to the difficulty experienced when assessing andcategorising the degree of instability and degeneration of theknee, a new tool has been developed to improve thedecision-making process and address the trepidation whencontemplating a specific arthroplasty. The quest for asolution to determine whether an arthroplasty is indicated,and the distinction between a TKA and PKA, has becomemore relevant in light of Riddle’s 20141 study that indicatesthe high, ‘inappropriate’ (34%) use of the TKA in the USA,without a conclusive algorithm of treatment. Willis-Owen in20092 asserted that 47% of knee arthroplasties are suitable forPKA rather than TKA but the various joint registries point toa high failure rate of the PKA despite better functionalscores3,4 and blame the infrequent user and inconsistentselection. The interpretation of data assessed is also aproblem as illustrated by Goodfellow in his critique aboutthe NZJR (2010).5
The history, clinical examination and routine X-rays withstress X-ray views to assess stability and degeneration,remain the cornerstone for evaluating a knee for PKA or aTKA.6,7 The goal is to determine whether the predominantsingle compartment degeneration presents with intactligaments, whether anteromedial degenerative pathology in
the varus deformed knee8 is present, and whether lateralvalgus deformity is suitable for PKA, or to illustratebicondylar degeneration suitable for a TKA. The X-raysassess wear and knee ligament integrity, e.g. the anteriorcruciate ligament (ACL) wear pattern as evaluated by Keys9
and Deschamps,10 and stability on the stress views.7
The PKA treatment option has regained popularity due tothe improved surgical technique, mini-incision approach,preservation of the ligaments, bone stock and appropriateinstrumentation.11-13 Excellent outcomes have been achievedby centres that have refined the selection and surgicaltechnique.14-18 The fully congruent mobile PKA demon-strated better functional results2,19 and 20-year surgicalresults comparable to that of the TKA20-24 with age, obesitylevel, state of the patellofemoral joint (PFJ) and chondrocal-cinosis not being regarded as contraindications.25,26 Theresults of PKA revision surgery to a TKA are controversialalthough they are compared with a primary TKA and not toa revision TKA.27,28 Overall risk of complications with PKA is4.3% and with TKA 11.4% (Oxford Group).19
Article summaryArticle focus1. Evaluation of the reproducibility of the X-KIDS as a ‘diagnostic tool’ with the specified X-ray sequence.2. X-KIDS correlation with the selected surgical procedure and the clinical influence.3. X-KIDS comparison with the stress views as a stand-alone test.4. The incidence of significant OA of the patellofemoral joint on the lateral view.
Key messages1. The X-KIDS is a reliable tool when contemplating a knee arthroplasty procedure.2. The X-KIDS classifies the degree of degeneration and instability. 3. The study confirms that the stress test as a ‘stand-alone tool’ is not reliable.4. Patellofemoral joint (PFJ) degeneration, in this series, is not a dominant decider for PKA/TKA.
BackgroundThe score should be considered with the patients’ clinical requirements and preferences.
The score is reliable, inexpensive and reproducible with two ‘new’ observations which illuminate the wearpattern of the ‘unstable’ degenerative knee. These propose that the 45° Rosenberg view is more reliable whenillustrating lateral pathology (rather than the stress view) and the ‘wedge sign’ for evaluating the integrity of thehealthy compartment. The co-contributors were a combination of medical specialists, namely a radiologist (20years’ experience), neurosurgeon (9 years), two orthopaedic surgeons (24 and 3 years respectively) and a non-medical volunteer, all of whom, apart from the corresponding author, were blinded to the implementedprocedure.
The author acknowledges that the co-contributors’ reviews were retrospective; however, their evaluations werenot focused on any surgical intervention. The X-KIDS may give false results due to the quality of the X-ray viewsand their possible misinterpretation together with ‘fresh’ ligament injuries as the X-ray features develop overtime with the subluxation effect only visible after the subsequent failure of the secondary stabilisers. Theperformance of the X-KIDS may be biased by the author’s understanding of the radiographic significance, whichmay have increased the concordance and it therefore requires further validation in other academic centres.
A new tool has been developed to improve the decision-making process and address the trepidation when
contemplating a specific arthroplasty
SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3 Page 63
The PFJ degeneration is rarely seen to alter theoutcome of the TKA or the PKA.23,24 In the NJR (Englandand Wales) of 2013,26 singular PFJ replacementsamounted to 1% of all replacements and more oftenoccurred in female patients (70% at an average age of 59years), compared with the TKA at 69 years. Thepreference for resurfacing the PFJ in TKA was 7% ofcementless procedures and 38% in cemented versions.
By improving the selection algorithm with the correctindication and surgical technique, an excellent long-term functional outcome for an arthroplasty can beachieved, suitable for the patient’s requirements.
MethodThe study reviewed 335 patients over a 3-year period ina knee clinic with the X-KIDS sequence, and comparedthe results with the stress views as a stand-alone and theprocedure implemented. Comparative studies of theoutcome of whether the X-KIDS were used or not, arenot available. The author correlated the X-rayappearance with the intra-operative findings and thesurgical decision.
The cornerstone of the X-KIDS is bone-on-bone wear andwas developed by allocating points to features normallyfound and easily recognised on routine knee X-rays. Thefeatures are narrowing (N), osteophyte formation (O) andsubluxation (S). The features are common to knee degen-eration and the weighting allocated according to theseverity of degeneration when each compartment isindividually assessed for bone-on-bone wear ornarrowing. The weighting is also applied to the instabilityfeatures as seen on the AP and lateral views.8,9
X-ray observer factors, namely osteophytes (bonyprojections at the margins of the joint)29 and subluxations(shifting out from the normal position), are included inthe score as they have a bearing on the wear and insta-bility assessment. This can unnecessarily affect thedecision for a specific procedure if not assessed.
Surgical decisions were taken which did notconform to the score preference and this will beexplained, e.g. a TKA was done when the scoreindicated suitability for a PKA due to excessivevalgus (clinical contraindication for PKA > 15°)(Table I).
Although the PFJ was not the focus of this studyand rarely influences the decision in arthroplastyas confirmed by Pandit and Beard,23-25 the joint wasevaluated on the lateral view by three observers asa separate study of 330 of the X-ray sequences toassess ‘significant’ PFJ degeneration. Skylineviews would be preferable in a follow-up studybut could not be done due to the extra costsinvolved.
The long-term results of the surgical cases cannotyet be assessed but the average time sinceoperation is 26.7 months.
Radiographic imaging1) Standing antero-posterior (AP) and lateral (LAT) of
the knee (Figure 1)2) PA 15° Rosenberg – medial wear (Figure 2a)3) PA 45° Rosenberg – lateral wear (Figures 2b and 7b)4) Varus stress view in 20° flexion (Figures 3 and 4)
1. Narrowing (N) (point count = medial 3; lateral 3) = 6(Figures 1, 2a, 2b, 3, 7)Bone-on-bone contact between the femoral condyleand the tibial surface suitable for arthroplasty attracts3 points (joint line narrowing). The contralateral jointmust be >5 mm (= 2.5 mm on femur and tibia) andparallel and if less attracts 3 points and precludes thePKA option.6,30-33
2. Osteophytes (O) (point count = medial 1 or lateral 1) =1 in total (Figures 1, 2a, 2b, 3, 4)This may be evident on femoral and tibial marginswith one point given medially or laterally, irrespectiveof the degree. These ‘spurs’ may reflect degenerationand extra-articular traction due to ‘laxity’ of theligaments caused by pseudo-instability.34
3. Subluxation (S) (point count = AP 1 and lateral 2) = 3(Figures 4 and 5)AP view: Subluxation with increasing varus andincreasing valgus is seen due to excessive wear in themedial or lateral compartments and the loss ofligament integrity. This attracts a single point but ifreduced on the stress view and the healthy joint ismaintained >5 mm and parallel, it is subtracted fromthe accumulated total (Figure 4).
Assessed points: N3O1S1 = 5 − 1 = 4 points
Lateral view: Anterior subluxation of the tibia andposterior wear of the medial tibial plateau as seen withACL deficiency (Figure 5)
Table I: Reasons for alternative treatment to score for PKA (includespatients’ and clinical preferences)Clinical factors Outcome
A: 4.77% Scored as PKA by evaluators and received a TKA (n = 16)5: Instability of ACL (not assessed on X-ray)3: Arthroscopy pre-arthroplasty3: Valgus >15 degrees3: Wanted TKA 1: Patella non-union and Lat. OA1: PFJ OA and med OA
B: 2.8% Scored as TKA by evaluators and received an PKA (n = 10)3: ACL deficient - (Fixed Bearing PKA)1: Young patient (ballet dancer)2: Posterior wear (medial ACL intact) PKA1: ACL deficient (lat. PKA and ACL recon.)3: ACL deficient (med. PKA and ACL recon.)
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Figure 1. AP & Lateral view - Varus
Figure 2a. Varus knee 15º PAFigure 2b. Valgus knee 45º PA
a b
Figure 3a. Varus stress Figure 3b. Valgus stress
Figure 4. AP subluxation and reduction Figure 5. Lateral subluxation
When there is a healthy weight-bearing compartment with
anterior subluxation of the tibia which can be rectified and
stabilised with an ACL reconstruction, the 2 points
assessed can be subtracted and can become suitable for a
PKA if an ACL reconstruction is done.
Example of assessed points:
N3O1S2 = 6 − 2 = 4 points
a b
Normal Subluxation
The 45° Rosenberg view evaluates the lateral compartment
with, specifically, the predilection for central and posterior
wear and the 15° Rosenberg displays the anteromedial
pathology (Figures 2, 7a and 7b).34,35
On the stress views the normal compartment must
maintain a parallel space of more than 5 mm which relates
to 2.5 mm of cartilage on the femur and tibia respectively
(Figures 1, 2, 3 and 6).29,33,36-38 If the healthy compartment
does not maintain the parallel opposing surfaces
(indicating normal cartilage, correctable intra-articular
varus, an intact collateral MCL/LCL32 and ACL) and
becomes angled, the knee should be regarded as a risk for
PKA (‘wedge sign’) (Figure 6).
It is important to prevent rotation and magnification ofthe knee during the stress views.
Anteromedial wear (varus Figures 2a, 2b and 3)
Confirm bone-on-bone wear and the integrity of the lateral
joint space with the stress views. The 15° PA is reliable but
does not confirm the integrity of the lateral joint space.37
Lateral wear (valgus Figures 2a, 2b, 3, 7a and 7b)
Confirm the lateral compartment wear pattern with the
45° PA. The 20° stress views are best used to confirm the
medial joint space retention.
Stress views in 20° flexion do not demonstrate the patho-
logical lateral compartment as reliably, due to the wear
pattern laterally being central and often posterior (on the
20° flexion views, the intact antero-lateral tibial cartilage is
stressed and this compartment can appear to be intact
Figure 7).
Scoring formulaA maximum of 10 points can be accrued with the X-KIDS
(N33 + O1 + S1
2).
1. X-KIDS of 3 and 4 points = PKA (mobile preferred or
fixed).
2. X-KIDS of 5 is considered for a PKA (mobile or fixed)
(NB clinical findings and surgical corrections).
3. X-KIDS > 5 points a TKA is indicated.
SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3 Page 65
Figures 6a and 6b. ‘Wedge sign’
a b
Figure 7. Valgus knee (same patient)
The cornerstone of the X-KIDS is bone-on-bone wear and was developed by allocating points to features normally
found and easily recognised on routine knee X-rays
Stress view not conclusive 45º Rosenberg conclusive
Page 66 SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3
ResultsThe average age of the 335 patients was 64 years (± SD of 10years) and the majority were female (54.8%). The averageage of the female patients (n = 184) was 65 ± 9 years and forthe male patients (n = 151) 63 ± 9.3 years. The actual PKAaccounted for 77.9% (n = 261) (98.9% mobile and 1.1% fixedbearing) of the procedures performed and the actual TKAfor 22.1% (n = 74).
The cohort composition is due to the surgeon being areferral centre for predominantly PKA procedures (see Table II).
1. In 95.82% of the cases the X-KIDS achieved consensuswith all five of the evaluators as they agreed on theprocedure to be performed based on the X-KID Scorecalculated. The agreement of multiple evaluators isrecapitulated with Light’s Kappa of 0.872 (bootstrappedCI95% [0.819; 0.912]). This indicates almost absoluteagreement between evaluators. In 2.98% of the cases theX-KIDS was incorrect in predicting the actual procedurerequired (undetected ACL deficiency and arthroscopedecision).
2. The score failed in ten patients (2.98%) (eight undiag-nosed ACL and two incorrectly diagnosed ACL).Twenty-six (26/336 = 7.38%) patients did not receive theprocedure according to the score. This was influenced bythe patients’ preferences and pre-operative clinicalfactors, e.g. pre-operative arthroscopic pathologicaldecisions (three), pre-operative PKA contraindications(five), instability of ACL which received a reconstructionACL and mobile PKA (three) or a fixed-bearing PKA(three) (Table I). In 16 (4.77%) cases the evaluators scoreda PKA but a TKA was performed. In ten (2.98%) casesthe evaluators scored a TKA but a PKA was performed.The agreement between the X-KIDS and the actualprocedure is recapitulated with Cohen’s Kappa of 0.753(bootstrapped CI95% [0.674; 0.834]). Since an indeter-minate score does not agree with any actual procedure,the measure is conservatively estimated. This indicatessubstantial, but not absolute agreement (see Table I).
3. A discrepancy between the X-KIDS and the stress testassessment as a stand-alone test was observed in 31(9.23%) of the 335 cases. In 5.97% of the 335 cases thediscrepancy was due to the non-detection of ACLdeficiency (n = 20) and 3.27% was due to clinical exclu-sions not detected (n = 11). As the ACL efficiency groupis routinely treated with a TKA this comprises a failurerate of 27.03% (20 out of 74 patients receiving TKA).
The Cohen’s Kappa between the stress test assessmentand the actual procedure is 0.699 (bootstrapped CI95%[0.592; 0.790]). Although still substantial, the level ofagreement is less than the level of agreement betweenthe X-KIDS and the actual procedure.
4. ‘Significant’ PFJ changes of 330 patients wereconsidered and 46.67% of the cases presented withsignificant changes. In the PKA group 41.40% (n = 106)of the 256 patients presented with PFJ degeneratechanges. This is significantly lower than the TKAgroup where 64.86% (n = 48) of the 74 patientspresented with significant changes (p = 0.0003, one-tailed Fisher’s Exact Test). Significant PFJ OA changesdid not influence the PKA decision.
5. Four failures were treated after 24 months: 1 medialPKA treated after traumatic ACL rupture with athicker bearing; and 3 medial PKA procedures treatedwith lateral PKAs.
Discussion There have been attempts to classify knee osteoarthritis,e.g. the initial Kellgren–Lawrence 1957 classification,39
Ahlback (1968),38 the Atlas of Line Drawings by NagaosaClassification 2000,40 the more modern imaging scoring(Whole Organ Magnetic Resonance Imaging Score‘WORMS’),41 and the Boston Leeds Osteoarthritis KneeScore (BLOKS)(2010)31 have been devised. There are theproponents of MRI-only visualisation, e.g. Guermazi(2011)32 and the comparative studies done by JeffreyDuryea (2001)30 on radiographic joint space width to thecartilage morphometry.
The conclusion drawn is that the two are comparablebut the ‘gold standard’ is still X-ray imaging.
The X-KIDS is different from all the previous evalu-ation systems, as it incorporates the stability of the kneeligaments and the severity of the weight-bearing degen-eration. This can assist the surgeon to improve hisdecision for a specific arthroplasty which will lead tooptimal treatment. The X-KIDS can be used as a classifi-cation of degenerative knee pathology and a reference toimprove research on arthroplasty selection.
The stress test as a stand-alone tool is unreliable indetecting the required procedure as it cannot evaluateACL deficiency adequately.
The PFJ rarely determined the procedure implemented.Only one clinically painful PFJ had a TKA (1/335) whenscored for a PKA.
Table II: X-KID Score versus the actual procedure performed
Outcome n F %
X-KID Score: Evaluator consensus with the procedure required 335 321 95.53%
X-KID Score: Received the procedure scored 335 310 92.3%
SA Orthopaedic Journal Spring 2015 | Vol 14 • No 3 Page 67
The X-KIDS must be understood and applied with dueconsideration to the clinical indications and contraindica-tions for the PKA and TKA and when used appropriately,the X-KIDS is more than 95% reliable and confirms theappropriate surgical intervention in at least 92% of kneesevaluated.
This research received no grant from any funding agency in thepublic, commercial or not-for-profit sectors.Affiliations: Dr CR Oosthuizen is a consultant to Biomet (SA)and Mathys (Swiss).
AcknowledgementsAs evaluators: Dr RP Goldschmidt, Dr D Vermaak, Dr SBurger, Dr CR Oosthuizen, Mr R SpangenbergAs Statistical Consulting Services: Maryn Viljoen
AppendixPlease take note of Appendix 1 and 2 after the originalarticle for further clarification.
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This article is also available online on the SAOA website(www.saoa.org.za) and the SciELO website (www.scielo.org.za).Follow the directions on the Contents page of this journal toaccess it.
Appendix 1
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Appendix 2
The X-ray knee instability and degenerative score (X-KIDS) X-ray score for knee arthroplasty
This is a surgical tool to aid the surgeon in the decision-making process. It does not replace clinical evaluation. This score is only applicable to the medial and lateral knee compartments.The score does not consider the patellofemoral joint degeneration.
SCORE 0 – 10< 5 Suitable for PKA (fixed or mobile)> 5 Suitable for TKA= 5 Can be suitable for PKA/TKA
Three X-ray signs are used with values:
1.Narrowing (N) - An affected compartment must be bone on bone – 3 points
(N )The unaffected compartment must be > 5 mm: – if not, 3 points
2. Osteophytes (O) - On the unaffected compartment – 1 point (O )3. Subluxation(S) - AP view and LAT view. AP view – 1 point; LAT view – 2 points (S )X-ray views for evaluation:1. Standing AP, LAT 2. Rosenberg views 15° PA (medial) 45° PA (lateral)
Better than stress for lateral OA.3. Valgus and varus stress view in 20° flexion
Better suited for medial OA.
(The joint line must remain parallel in this view and > 5 mm)
NB. Extra-articular ‘lipping’ (osteophytes) does not compromise the weight-bearing surface.
N + O + S = 101. Score = 3 = Full thickness loss of cartilage narrowing (N ) in one compartment.
2. Score = 4 = Narrowing (N ) with medial/lateral osteophytes (O ) or AP subluxation (S )
3.
Score = 5 = Narrowing (N ) with medial/lateral osteophytes (O ) and AP subluxation (S )
A score of 4 or 5 can obtain a −1 subtraction if the subluxation (S ) on the AP view can be reduced on stress views (score 5−1=4; see Score Card).
4. Score = 5 = Narrowing (N ) with lateral view subluxation. (S ) (ACL deficient)
5. Score 6 or 7 due to S ; can subtract 2 points with reconstruction of ACL and then PKA can be done.
NB. When evaluating the unaffected compartment, it needs to retain >5 mm of space and stay parallel to the opposing jointsurface on the stress views. The ‘wedge sign’ of a ‘healthy’ compartment is a contraindication for a partial knee replacement.
![1)LSG-TKA&LCS [PKGC 22-25Nov09]](https://static.documents.pub/doc/80x56/577daae31a28ab223f8b8ab1/1lsg-tkalcs-pkgc-22-25nov09.jpg)
